1. Field of the Invention
The present invention relates to an objective lens system for use in a single lens reflex camera, and more particularly to an inverted telephoto objective lens system of a 5-component, 5-lens element type.
2. Description of the Prior Art
Various inverted telephoto type lens systems of a 5-component, 5-lens element construction have been provided as wide angle objective lens systems for use with single lens reflex cameras. These lens systems are known from an optical designer viewpoint, as the simplest construction of lenses. Generally, they consist of, from the object side, a first negative lens, a second positive lens, third negative lens, a fourth positive lens and a fifth positive lens. An example of such a lens can be found in U.S. Pat. No. 3,936,153 which proposes an inverted telephoto type lens system of a 5-component, 5-lens element design which has a field angle of 64.degree., an aperture ratio of 1/2.8, a back focal distance of approximately the focal length of the whole lens system and a good image forming capability which is at least equal to or better than that of the conventional inverted telephoto-type lens system comprising six or seven lenses.
Other examples of prior art can be found in U.S. Pat. No. 3,731,989, U.S. Pat. No. 4,203,653, Japanese Laid Open Patent Applications Nos. 51-56625, 51-75440, 52-131718, 53-59418, and 55-147607 and finally in Japanese Patent Publication No. 46-24194.
However, in a wide angle objective lens system consisting of a few lens elements such as a 5-component, 5-element-type, it becomes increasingly difficult to maintain both a desired aperture ratio and good image forming capability in direct proportion to the increase in the field angle and in the back focal distance.
Thus, the prior art is still seeking to provide a simplified lens construction with improved performance capabilities.